High-pressure granulites from Cariré, Borborema Province, NE Brazil: Tectonic setting, metamorphic conditions and U–Pb, Lu–Hf and Sm–Nd geochronology

Abstract

In the northwest region of the Ceará Central Domain, Borborema Province, an elongate area of mylonitic diorites and granodiorites is structurally controlled by NE–SW-trending strike-slip faults. Granitic material and layers and lenses of felsic and mafic granulites occur along the main shear zones. We present and discuss petrographic, geothermobarometric, and geochronological (LA-MC-ICPMS U–Pb and Lu–Hf in zircon and Sm–Nd whole-rock) data for these rocks. Felsic granulites are composed of orthopyroxene+clinopyroxene+plagioclase+quartz±hornblende±garnet±biotite±feldspar, while the mafic granulites comprise clinopyroxene+plagioclase+garnet+hornblende±rutile±quartz. The P–T conditions recorded range from 9.4 to 8.3kbars and from 804 to 870°C for the felsic granulites and from 13.6 to 10.2kbars and 910 to 750°C for the mafic granulites. U–Pb zircon ages of granodiorite host rocks are 2157 and 2044Ma. The felsic granulites yield a U–Pb age of 2110Ma, while the mafic granulites yield U–Pb zircon ages of 613 and 589Ma for the metamorphic recrystallization. Sm–Nd and Lu–Hf TDM ages for the mafic granulites are similar (1.6–1.3Ga) and share positive values of εNd and εHf, which suggests that these mafic rocks were derived from a juvenile Mesoproterozoic crust. In addition, the felsic granulites and the granodiorites have similar TDM-Nd and U–Pb ages (with positive values of εNd), indicating a Paleoproterozoic mantle source for these rocks.